"Most widely used" seems a bit strong... https://www.google.co.uk/search?q=cbt https://www.google.co.uk/search?q=cbt (just in the interest of full disclosure,

"Most widely used" seems a bit strong... https://www.google.co.uk/search?q=cbt https://www.google.co.uk/search?q=cbt (just in the interest of full disclosure, I'm the lead developer for Sleepio)